Why instance variables can be modified through a field reader with the << operator?
1
Consider the following class.
class Test
attr_reader :word
def initialize(word)
@word = word
end
def append_word(token)
word << token
end
end
Consider a sample usage of the class.
2.4.0 :001 > t = Test.new('Hello')
=> #<Test:0x007f7f09902970 @word="Hello">
2.4.0 :002 > t.append_word(' world!')
=> "Hello world!"
2.4.0 :003 > t.word
=> "Hello world!"
2.4.0 :004 >
I am new to Ruby. I don't understand why I can use the append_word instance method to modify the instance variable @word of a Test instance. word in append_word seems to be a field reader. My understanding is that a field reader is for reading only. How can word << token in append_word modify the value of @word in a Test instance?
ruby
asked Nov 13 '18 at 3:09
Isaac ToIsaac To
1057
add a comment |
1
Consider the following class.
class Test
attr_reader :word
def initialize(word)
@word = word
end
def append_word(token)
word << token
end
end
Consider a sample usage of the class.
2.4.0 :001 > t = Test.new('Hello')
=> #<Test:0x007f7f09902970 @word="Hello">
2.4.0 :002 > t.append_word(' world!')
=> "Hello world!"
2.4.0 :003 > t.word
=> "Hello world!"
2.4.0 :004 >
I am new to Ruby. I don't understand why I can use the append_word instance method to modify the instance variable @word of a Test instance. word in append_word seems to be a field reader. My understanding is that a field reader is for reading only. How can word << token in append_word modify the value of @word in a Test instance?
ruby
asked Nov 13 '18 at 3:09
Isaac ToIsaac To
1057
add a comment |
1
1
1
Consider the following class.
class Test
attr_reader :word
def initialize(word)
@word = word
end
def append_word(token)
word << token
end
end
Consider a sample usage of the class.
2.4.0 :001 > t = Test.new('Hello')
=> #<Test:0x007f7f09902970 @word="Hello">
2.4.0 :002 > t.append_word(' world!')
=> "Hello world!"
2.4.0 :003 > t.word
=> "Hello world!"
2.4.0 :004 >
I am new to Ruby. I don't understand why I can use the append_word instance method to modify the instance variable @word of a Test instance. word in append_word seems to be a field reader. My understanding is that a field reader is for reading only. How can word << token in append_word modify the value of @word in a Test instance?
ruby
asked Nov 13 '18 at 3:09
Isaac ToIsaac To
1057
Consider the following class.
class Test
attr_reader :word
def initialize(word)
@word = word
end
def append_word(token)
word << token
end
end
Consider a sample usage of the class.
2.4.0 :001 > t = Test.new('Hello')
=> #<Test:0x007f7f09902970 @word="Hello">
2.4.0 :002 > t.append_word(' world!')
=> "Hello world!"
2.4.0 :003 > t.word
=> "Hello world!"
2.4.0 :004 >
I am new to Ruby. I don't understand why I can use the append_word instance method to modify the instance variable @word of a Test instance. word in append_word seems to be a field reader. My understanding is that a field reader is for reading only. How can word << token in append_word modify the value of @word in a Test instance?
ruby
ruby
asked Nov 13 '18 at 3:09
Isaac ToIsaac To
1057
asked Nov 13 '18 at 3:09
Isaac ToIsaac To
1057
asked Nov 13 '18 at 3:09
Isaac ToIsaac To
1057
asked Nov 13 '18 at 3:09
Isaac ToIsaac To
1057
asked Nov 13 '18 at 3:09
Isaac ToIsaac To
1057
1057
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
5
Your @word references an object in memory. This object happens to be a Hello! string. Your class does not allow to (easily) set a new object for your @word instance variable, but nothing currently stops you from modifying the object directly. If you wish for the object to not be modifiable, you could .freeze it:
class Test
attr_reader :word
def initialize(word)
@word = word.freeze
end
def append_word(token)
word << token
end
end
> Test.new("Hello").append_word("world!")
# FrozenError (can't modify frozen String)
answered Nov 13 '18 at 3:13
Marcin KołodziejMarcin Kołodziej
4,5001315
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee thatword, the field reader, refers to the exact same object referred by@wordinstead of a copy of the object referred by@word?
– Isaac To
Nov 13 '18 at 6:43
Yes,attr_reader :wordis the same asdef word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if@wordis a small integer,wordwill return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.
– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling@wordalso returns a copy of@word, therefore adding aattr_readerdoes not really change how you interact with underlying value.
– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
|
show 3 more comments
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
5
Your @word references an object in memory. This object happens to be a Hello! string. Your class does not allow to (easily) set a new object for your @word instance variable, but nothing currently stops you from modifying the object directly. If you wish for the object to not be modifiable, you could .freeze it:
class Test
attr_reader :word
def initialize(word)
@word = word.freeze
end
def append_word(token)
word << token
end
end
> Test.new("Hello").append_word("world!")
# FrozenError (can't modify frozen String)
answered Nov 13 '18 at 3:13
Marcin KołodziejMarcin Kołodziej
4,5001315
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee thatword, the field reader, refers to the exact same object referred by@wordinstead of a copy of the object referred by@word?
– Isaac To
Nov 13 '18 at 6:43
Yes,attr_reader :wordis the same asdef word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if@wordis a small integer,wordwill return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.
– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling@wordalso returns a copy of@word, therefore adding aattr_readerdoes not really change how you interact with underlying value.
– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
|
show 3 more comments
5
Your @word references an object in memory. This object happens to be a Hello! string. Your class does not allow to (easily) set a new object for your @word instance variable, but nothing currently stops you from modifying the object directly. If you wish for the object to not be modifiable, you could .freeze it:
class Test
attr_reader :word
def initialize(word)
@word = word.freeze
end
def append_word(token)
word << token
end
end
> Test.new("Hello").append_word("world!")
# FrozenError (can't modify frozen String)
answered Nov 13 '18 at 3:13
Marcin KołodziejMarcin Kołodziej
4,5001315
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee thatword, the field reader, refers to the exact same object referred by@wordinstead of a copy of the object referred by@word?
– Isaac To
Nov 13 '18 at 6:43
Yes,attr_reader :wordis the same asdef word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if@wordis a small integer,wordwill return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.
– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling@wordalso returns a copy of@word, therefore adding aattr_readerdoes not really change how you interact with underlying value.
– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
|
show 3 more comments
5
5
5
Your @word references an object in memory. This object happens to be a Hello! string. Your class does not allow to (easily) set a new object for your @word instance variable, but nothing currently stops you from modifying the object directly. If you wish for the object to not be modifiable, you could .freeze it:
class Test
attr_reader :word
def initialize(word)
@word = word.freeze
end
def append_word(token)
word << token
end
end
> Test.new("Hello").append_word("world!")
# FrozenError (can't modify frozen String)
answered Nov 13 '18 at 3:13
Marcin KołodziejMarcin Kołodziej
4,5001315
Your @word references an object in memory. This object happens to be a Hello! string. Your class does not allow to (easily) set a new object for your @word instance variable, but nothing currently stops you from modifying the object directly. If you wish for the object to not be modifiable, you could .freeze it:
class Test
attr_reader :word
def initialize(word)
@word = word.freeze
end
def append_word(token)
word << token
end
end
> Test.new("Hello").append_word("world!")
# FrozenError (can't modify frozen String)
answered Nov 13 '18 at 3:13
Marcin KołodziejMarcin Kołodziej
4,5001315
answered Nov 13 '18 at 3:13
Marcin KołodziejMarcin Kołodziej
4,5001315
answered Nov 13 '18 at 3:13
Marcin KołodziejMarcin Kołodziej
4,5001315
answered Nov 13 '18 at 3:13
Marcin KołodziejMarcin Kołodziej
4,5001315
4,5001315
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee thatword, the field reader, refers to the exact same object referred by@wordinstead of a copy of the object referred by@word?
– Isaac To
Nov 13 '18 at 6:43
Yes,attr_reader :wordis the same asdef word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if@wordis a small integer,wordwill return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.
– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling@wordalso returns a copy of@word, therefore adding aattr_readerdoes not really change how you interact with underlying value.
– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
|
show 3 more comments
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee thatword, the field reader, refers to the exact same object referred by@wordinstead of a copy of the object referred by@word?
– Isaac To
Nov 13 '18 at 6:43
Yes,attr_reader :wordis the same asdef word; @word; end
– Marcin Kołodziej
Nov 13 '18 at 6:44
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if@wordis a small integer,wordwill return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.
– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling@wordalso returns a copy of@word, therefore adding aattr_readerdoes not really change how you interact with underlying value.
– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee that
word, the field reader, refers to the exact same object referred by @word instead of a copy of the object referred by @word?– Isaac To
Nov 13 '18 at 6:43
Thanks. Your post answered my question. However, it brought up another. Does Ruby guarantee that
word, the field reader, refers to the exact same object referred by @word instead of a copy of the object referred by @word?– Isaac To
Nov 13 '18 at 6:43
Yes,
attr_reader :word is the same as def word; @word; end– Marcin Kołodziej
Nov 13 '18 at 6:44
Yes,
attr_reader :word is the same as def word; @word; end– Marcin Kołodziej
Nov 13 '18 at 6:44
1
1
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if
@word is a small integer, word will return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.– Amadan
Nov 13 '18 at 7:15
Technically, Ruby does have some types that are not full objects (by the fact their values are not references), though they behave as objects for most intents and purposes. For example, if
@word is a small integer, word will return a copy and not a reference (as these objects are never referenced). However, since all such quasi-objects are immutable, there is no situation where a copy will behave differently than a reference, so it's a moot point.– Amadan
Nov 13 '18 at 7:15
@Amadan true, also worth mentioning that in case of these immutable objects, calling
@word also returns a copy of @word, therefore adding a attr_reader does not really change how you interact with underlying value.– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan true, also worth mentioning that in case of these immutable objects, calling
@word also returns a copy of @word, therefore adding a attr_reader does not really change how you interact with underlying value.– Marcin Kołodziej
Nov 13 '18 at 13:56
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
@Amadan Does Ruby guarantee that all mutable objects are passed by reference?
– Isaac To
Nov 13 '18 at 22:32
|
show 3 more comments
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